A through-silicon-via, or TSV, provides electrical continuity between the top and bottom surfaces of a semiconductor chip. A TSV is fabricated by deep etching into the silicon wafer, or substrate that comprises the semiconductor chip, and filling the resulting hole with a liner and a metal filling. The silicon substrate is then ground, or thinned, from the backside until the metal filling is exposed, and backside metal (BSM) is disposed on the thinned backside surface for electrical contact. If the silicon is not etched deeply enough, the TSV may be defective. However, the TSV is not electrically functional before silicon thinning and BSM deposition are completed, therefore, conventional inline electrical testing cannot be used to determine whether the TSV is defective until these steps are completed. It is therefore desirable to have an improved inline measurement of through-silicon via depth.